1. Field of the Invention
The present invention relates to an ocular light stimulus apparatus, and more particularly relates to an ocular light stimulus apparatus in which the ocular fundus of an examinee's eye is irradiated with ocular fundus observation light to observe the ocular fundus and is irradiated with background light and stimulus light to locally stimulate the retina with the stimulus light and perform a biological examination using a bioelectrical signal obtained from the retina.
2. Description of the Prior Art
Conventional known methods used primarily for ophthalmological examination include not only capturing a fundus image and performing fundus examination, but also electroretinogram (ERG) examination in which stimulus light is projected onto a retina to measure an action potential generated in the retina, and an electroretinogram is created to perform an ophthalmological biological examination.
In an ERG examination, the ocular fundus is irradiated with visible stimulus light, and the background irradiated with the stimulus light has to be illuminated by background light. A suitable combination of the intensity of the background light and the intensity of the stimulus light affects the quality of the ERG examination. When the stimulus light is projected locally (local ERG) on a macular spot of the ocular fundus to perform the ERG examination, the background light is projected as visible light onto the ocular fundus.
The background light is projected, e.g., from between an objective lens and an apertured mirror onto the ocular fundus via a half mirror (Journal of Japanese Ophthalmological Society, Vol. 85 (10) (Oct. 10, 1981, 9-(1521) to 19-(1531)).
According to the configuration disclosed in Japanese Laid-open Patent Application No. 2006-42952, the ocular fundus is irradiated with white light using a white light-emitting diode arranged in the observation optical system, and, with this as a background, a spot light is projected as stimulus light from a high-luminance light-emitting diode to perform a local ERG examination while the ocular fundus is observed using infrared light.
According to the configuration of WO2008/111166A1, a working distance light source may also be used as a background light source for a local ERG examination, and the visible light from the light source is projected as the background light onto the ocular fundus.
However, with a conventional local ERG examination, background light is projected from an illumination optical system or by using the effective outside diameter of a photographic stop. Therefore, the amount of background light directed onto the ocular fundus is varied by the pupil diameter of the eye to be examined, causing measurement error and making it difficult to perform an accurate local ERG examination.